Cerulean Warbler (Setophaga cerulea) Species Guidance Family: Parulidae – the wood-warblers State Status: Threatened (1989) State Rank: S2S3B Federal Status: None Global Rank: G4 Wildlife Action Plan Mean Risk Score: 4.1 Wildlife Action Plan Area of Counties with documented locations of Importance Score: 2 Cerulean Warbler breeding or breeding Photo by Dennis Malueg evidence in Wisconsin. Source: Natural Heritage Inventory Database, October 2018. Species Information General Description: The Cerulean Warbler is a small songbird (11.5 cm [4.5 in]) with long, pointed wings and a short tail. Sexes are dimorphic in both basic and alternate plumages. Both sexes have two broad white wing bars, white tail spots, and dark streaking down the side and flanks. Males have sky-blue head and upperparts, blackish wings and tail, blackish streaking on back, and narrow blue-gray chest band. Females have blue-green head and upperparts, a prominent pale supercilium (stripe above the eye), and underparts that are typically washed with pale yellow. Females also lack blackish streaking on the back. Immatures resemble females (Howell and Webb 1995, Dunn and Garrett 1997). The song is composed of three parts: a long introductory section and shorter middle section on the same pitch, followed by a final buzz on a higher pitch. Songs can be described as ZEE ZEE ZEE ZIZIZIZI ZZZEEET (Flaspohler 1993, Hamel 2000a). An example of a typical song can be heard here: <http://www.allaboutbirds.org/guide/Cerulean_Warbler/sounds> Definitive Identification: The upperparts of all but the immature females have distinctive bluish tones. The small size, short-tailed appearance, prominent supercilium, and absence of back streaks help to distinguish adult and immature female Cerulean Warblers from other similar species (Dunn and Garrett 1997). Similar Species: Females and immature male Cerulean Warblers resemble immature female Blackburnian Warblers (Setophaga fusca). However, immature Blackburnian Warblers have a longer tail and a darker, more triangular cheek patch than immature Cerulean Warblers. Also, immature Blackburnian Warblers generally appear buffy below, whereas immature Cerulean Warblers have whitish underparts washed with yellow (Dunn and Garrett 1997, Hamel 2000a). In Wisconsin, Cerulean and Blackburnian Warblers are more likely to co-occur during migration than during the breeding season. Additionally, Blackburnian Warblers prefer forest stands dominated by coniferous species whereas Cerulean Warblers prefer deciduous forest types. Associated Species: Within appropriate floodplain forest habitats in Wisconsin, Cerulean Warblers may occur with the following Species of Greatest Conservation Need: Yellow- crowned Night-Heron (Nyctanassa violacea), Red-shouldered Hawk (Buteo lineatus), Yellow-billed Cuckoo (Coccyzus americana), Kentucky Warbler (Geothlypis formosa), Yellow-throated Warbler (Setophaga dominica), and Prothonotary Warbler (Protonotaria citria). Within upland hardwood forest types, Cerulean Warblers can occur with the following Species of Greatest Conservation Need: Yellow-billed Cuckoo, Acadian Flycatcher (Empidonax virescens), Wood Thrush, Worm-eating Warbler (Helmitheros vermivorum), Louisiana Waterthrush (Seiurus motacilla), Kentucky Warbler, and Hooded Warbler (Wilsonia citrina). Cerulean Warbler Breeding Locations from Wisconsin’s Breeding Bird Atlas. (Cutright et al. 2006) Cerulean Warbler Species Guidance 1 of 8 PUB ER-677 (last updated October 8, 2018) State Distribution and Abundance: Cerulean Warblers breed sparingly throughout the southern three-fourths of the state, as indicated on map to the right (source: Cutright et al. 2006) and occur in scattered localities in the northern counties (Mossman 2006). Highest concentrations of this species occur in the Baraboo Hills, the floodplain and bluffside forests of the Lower Wisconsin and Mississippi River corridors, the Blue Hills, Straight Lake, both units of the Kettle Moraine State Forest, and in many scattered areas in the Western Coulee and Ridges Ecological Landscape, which needs more inventory (Flaspohler 1993, Mossman 2006). Distribution information for this species may not reflect its full extent in Wisconsin because many areas of the state have not been thoroughly surveyed. Global Distribution and Abundance: The Cerulean Warbler’s summer range extends eastward from the Great Plains in eastern North and South Dakota, Nebraska, Kansas, and Oklahoma; south to Arkansas, Mississippi, Tennessee, northern Alabama and Georgia, and South Carolina; north to Massachusetts, southern Quebec, southeastern Ontario, Michigan, Wisconsin, and central Minnesota. Within this range, highest densities occur in eastern Tennessee, eastern Kentucky, southern and western West Virginia, southeastern Ohio, and southwestern Pennsylvania (USFWS 2012). The winter range extends from northern Columbia and Venezuela south along a Global range map for Cerulean Warbler. narrow band of evergreen forest at approximately 500-2000m (1650-6550 ft) elevation (NatureServe 2013) in eastern Ecuador, eastern Peru, and northwestern Bolivia (Flaspohler 1993, USFWS 2007). Diet: Cerulean Warblers are primarily insectivorous, preferring bees and wasps (Hymenoptera), caterpillars (Lepidoptera), beetles (Coleoptera), and true bugs (Homoptera) (Hamel 2000b, USFWS 2012). Reproductive Cycle: Cerulean Warblers arrive in Wisconsin from late April to late May. Although Wisconsin breeding records are scarce due to the difficulty of finding nests, one nest with eggs was found on June 17, nests with young were documented from June 23 to July 1 (Robbins 1991), and adults feeding young were observed from June 20 to July 28 (Mossman 2006). Cerulean Warblers depart Wisconsin by late August (Robbins 1991). J F M A M J J A S O N D Overwintering Avoidance Overwintering (in the tropics) Period (in the tropics) Ecology: Cerulean Warblers forage in the upper canopy of mature hardwood forests and are more often heard than seen. Foraging heights range from 2-45m (6.5-150 ft), and average 15m (50 ft) in Tennessee and Arkansas (Hamel 2000a, b). This species gleans insects from the bases of leaves and small branches and, less commonly, hovers at the underside and outer edge of foliage (Hamel 2000a, USFWS 2012). Cerulean Warblers use a variety of trees for foraging and apparently do not prefer any specific tree species (Hamel 2000a). Cerulean Warblers are nocturnal migrants that fly more than 4000km (2500 miles) from eastern North America to northern South America (USFWS 2007). In the spring, they apparently depart the wintering grounds and move north through Panama, Costa Rica, and Belize, and then across the Gulf of Mexico to the Gulf Coast of the U.S., continuing on to their breeding grounds. This pattern is likely reversed during fall migration (Hamel 2000b). Nests are often built in large deciduous trees such as basswoods (Tilia americana), elms (Ulmus spp.), maples (Acer spp.), and especially oaks (Quercus spp.) at heights of 4.5-30m (15-100 ft), most commonly 10-20m (30-65 ft) (Hamel 2000b). Nests are built in the middle and upper branches and concealed from above by clumps of leaves from other branches or vines (Hamel 2000b, USFWS 2012). Female Cerulean Warblers build shallow cup-nests composed of fine grasses, plant fibers, bark strips, and weed stems (Flaspohler 1993). The female lays and incubates 2-5 eggs, and average clutch size is four. Incubation lasts from 11-12 days, with chicks fledging 9-11 days after hatching (Flaspohler 1993, Hamel 2000b). This species typically raises only one brood but may re-nest if the first attempt fails (Hamel 2000b). Cerulean Warbler Species Guidance 2 of 8 PUB ER-677 (last updated October 8, 2018) Natural Community Associations (WDNR 2005, WDNR 2009): Significant: floodplain forest, southern dry-mesic forest Moderate: oak woodland, southern mesic forest Minimal: none a b c Photos (left to right): a) Cerulean Warbler habitat in Sheboygan County, Rich Staffen, Wisconsin DNR; b) this large (>600 acres) block of dry-mesic forest in Grant County supports numerous breeding pairs of Cerulean Warbler and associated rare forest interior birds, Photo acquired in 2010; and c) Cerulean Warbler habitat in Columbia County. © B. Collins Habitat: The Cerulean Warbler breeds in wet-mesic to dry-mesic habitats that contain large deciduous trees (Flashpohler 1993, Mossman 2006). In Wisconsin, this species occurs in mature upland and lowland hardwood forests, especially oak-hickory and maple forest types (Mossman 2006). Habitat measures such as canopy cover, tree species composition, stand age, and tract size vary considerably across its range (Hamel 2000b). In eastern Ontario, male Cerulean Warbler territories were characterized by large trees approximately 15-17m (49-56 ft) tall and dense foliage cover (45% cover) in the 12-18m (39-59 ft) height category (Jones and Robertson 2001). In southeastern Ontario, nest trees had an average height of 17.7m (58 ft) and an average diameter at breast height (DBH) of 40.2cm (15.8 in) (Oliarnyk and Robertson 1996). In Wisconsin, Cerulean Warblers are more likely to occur in woodlots at least 200 acres (Temple 1988). In the Baraboo Hills, this species is associated with sites containing many large (>40 cm [15.7 in] DBH) trees, >65% canopy cover, and small canopy gaps (Mossman and Lange 1982). Threats: The largest threat to Cerulean Warblers comes from the fragmentation and loss of existing large patches of older deciduous forest (Flaspohler 1993), and the continuing decline of oaks, especially